Conventional seat belt retractors commonly include a frame including a base wall for attachment to a motor vehicle structure such as a pillar. The frame also has side walls with aligned apertures to receive a reel shaft which rotatably mounts a belt reel. A spring acts between the housing and the reel shaft to bias the reel in the direction to wind up the restraint belt. A lock bar extends between the housing side walls and is movable into engagement with a pair of sprockets carried by the belt reel to lock the reel against belt unwinding rotation.
A sensing mechanism is conventionally provided to lock up the reel by moving the lock bar into engagement with the reel sprockets. The sensing mechanism may be responsive to vehicle deceleration or to the rate of unwinding of belt from the reel. The vehicle sensitive locking mechanism traditionally includes a ball or pendulum which moves relative to the lock bar upon occurrence of a vehicle deceleration condition to move the lock bar to the locked condition. The belt sensitive locking mechanism conventionally includes a flywheel which is carried by the reel and lags behind rotation of the reel in response to a certain condition of belt unwinding to initiate movement of the lock bar to the locked position.
In conventional seat belt retractors the sensing mechanism, whether of the vehicle sensitive locking type or the belt sensitive locking type, is traditionally located on the outside of the frame side walls so that the sensing mechanism increases the overall physical dimensions of the retractor and therefore presents a design constraint to the mounting of the retractor within the motor vehicle. This design constraint is particularly severe in those retractors which employ both a vehicle sensitive locking mechanism and a belt sensitive locking mechanism.
Thus, it would be desirable to provide a seat belt retractor in which the sensing mechanism, whether vehicle sensitive, belt sensitive, or both, is situated entirely inside the reel.